1. Field of the Invention
The present invention relates to an LED (Light-Emitting Diode) light bar, and in particular to a method for manufacturing an LED light bar and an LED light bar thereof.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus of wide applications, such as mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens.
Most of the liquid crystal displays that are currently available in the market are backlighting liquid crystal displays, which comprise an enclosure, a liquid crystal panel arranged in the enclosure, and a backlight module mounted in the enclosure. The structure of a conventional liquid crystal panel is composed of a color filter (CF) substrate, a thin-film transistor (TFT) array substrate, and a liquid crystal layer arranged between the two substrates and the principle of operation is that a driving voltage is applied to the two glass substrates to control rotation of the liquid crystal molecules of the liquid crystal layer in order to refract out light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided from the backlight module in order to normally display images. Thus, the backlight module is one of the key components of the liquid crystal displays. The backlight modules can be classified in two types, namely a side-edge backlight module and a direct backlight module, according to the site where light gets incident. The direct backlight module comprises a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), which is arranged at the backside of the liquid crystal panel to form a planar light source directly supplied to the liquid crystal display panel. The side-edge backlight module comprises an LED light bar, serving as a backlight source, which is arranged at an edge of a backplane to be located rearward of one side of the liquid crystal display panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face at one side of the light guide plate and is projected out of a light emergence face of the light guide plate, after being reflected and diffused, to pass through an optic film assembly so as to form a planar light source for the liquid crystal display panel.
Heat dissipation has always been a primary factor that affects the lifespan of a liquid crystal display device. A major source of heat of a liquid crystal display device is generated by a backlight source. The backlight sources that are conventionally used are generally LED light bars. An LED light bar basically comprises a printed circuit board (PCB) and LED chips that are mounted on and electrically connected with the PCB. The cause that the LED light generates heat is that the electrical power supplied thereto has not been all converted into light energy and a fraction thereof is converted into thermal energy. A characteristic of the LED chip is that a huge amount of heat can be generated in an extremely small volume. The LED chip itself has a small thermal capacity so that the heat must be dissipated with the greatest speed, otherwise an extremely high junction temperature may result.
Heat dissipation of the LED chip is attracting more and more attention. This is because light decay or lifespan of an LED chip is directly associated with the junction temperature thereof. Poor heat dissipation leads to a high junction temperature and a short lifespan. According to Arrhenius Law, the lifespan would be extended by two times for every temperature drop of 10° C.
An LED light bar heat dissipation solution commonly adopted in a conventional liquid crystal display device is a heat dissipation plate arranged between a PCB and a backplane to transmit as efficiently as possible heat generated by an LED chip to the outside. However, such as heat dissipation solution is imperfect. If the heat dissipation plate is arranged to be a metal-made heat dissipation plate, then the weight of a backlight module would be increased.
Graphene is a novel type of material having advantages of temperature resistance, small thermal expansion coefficient, thermal conductivity, electrical conductivity, and small friction coefficient and can be attached to a curved surface or an irregular surface. Heat dissipation with grapheme shows relatively high horizontal thermal conductivity (see FIG. 1), enabling efficient conduction of energy in a horizontal direction to make uniform distribution of thermal energy over an enter surface in the horizontal direction and eliminating localized hot spots.
thermal conductivitymaterials(W/m · K)common metalssilver429copper401gold317aluminum237carbon basedGTS (Thermal Graphite Sheet)1500-1700materialsCNT (Carbon Nano Tube)3000-3500diamond1000-2200graphene4000-6000otherssilicone gel1-3
It can be seen from the above table that graphene has the largest thermal conductivity. Using graphene as a heat dissipation material for an LED light bar would greatly improve the performance of heat dissipation and extend the lifespan of the LED light bar thereby extending the lifespan of a liquid crystal display device using the LED light bar.